Conventionally, as means of supplying irrigation liquids such as water or liquid fertilizer to the plants to be grown on the soil in the agricultural land, the plantation or the like, drip irrigation apparatuses that regulate the supply speed of the irrigation liquid have been employed. The use of the drip irrigation apparatus enables the saving of the irrigation liquid and the management of the growth of the plants.
Such a drip irrigation apparatus includes a dripper for controlling the ejection amount of the irrigation liquid per unit time when ejecting the irrigation liquid having flowed into a flow tube from the water source side (pump side) toward the plants.
One example of such drip irrigation apparatuses is what is called an on-line dripper. The on-line dripper is used by being inserted into holes bored in a tube wall (side wall) of polyethylene pipe or into the opening of the end portion of a microtube. The on-line dripper is conveniently employed not only in soil culture but also in nutriculture or pot culture when used for greenhouse culture, raising seedling, fruit growing, and the like.
As such an on-line dripper, a dripper with what is called a differential pressure control mechanism (pressure correction function) being installed is known. The dripper is configured, for example, with a three-component structure in which an elastic film (e.g., silicone rubber film) such as a diaphragm is sandwiched by an inlet side member and an outlet side member (see PTLS 1 and 2, for example).
The dripper utilizes the operation of the diaphragm (film) in accordance with the liquid pressure of the irrigation liquid having flowed from the inlet of the dripper to control the inflow of the irrigation liquid toward a pressure reduction channel on the downstream side of the inlet and to control the amount of the outflow of the irrigation liquid from the outlet of the dripper after pressure reduction by the pressure reduction channel.
More specifically, in the dripper, when the inflow liquid pressure of the irrigation liquid toward the inlet is increased to a certain level, the diaphragm that is disposed to shield the pressure reduction channel is deflected by the inflow liquid pressure toward the outlet. Due to the deformation of the diaphragm, the reduction pressure channel is opened, and thus the irrigation liquid flows into the pressure reduction channel. The irrigation liquid having flowed into the pressure reduction channel moves toward the outlet while the pressure of the irrigation liquid is reduced in the pressure reduction channel to flow out of the dripper from the outlet. When the inflow liquid pressure toward the inlet is further increased, the amount of the deflection of the diaphragm toward the outlet becomes larger. In association with the larger amount of the deflection of the diaphragm, the sectional size of the channel at the outlet is reduced, and thus the outflow of the irrigation liquid is regulated.